DC motors have found wide use in automotive applications. It is not uncommon to find DC motors used in the window lift mechanism, seat lift mechanism, sun roof controls, door locks, trunk pull-down assemblies etc. In at least some of these applications, electrical current protection must be provided to the DC motor in order to prevent excessive current draw through the motor or motor control circuit during the motor stall or highly loaded conditions. If some type of current protection is not provided in the DC motor circuit, it is possible that under the stall or highly loaded conditions, the motor will draw sufficient current to destroy either itself, portions of the motor control circuit, or both.
Another common use for DC motors in automotive applications is in windshield wiper assemblies where it is common to employ a DC motor for driving the windshield wipers of the vehicle. Because windshield wiper systems must typically operate in a number of modes (such as park mode, retract mode, high speed, low speed, etc.), the control systems for windshield wiper DC motors tend to be some of the most complex motor control systems found in automotive applications. The systems often utilizes a kinematic linkage between the motor drive shaft and the wiper arm drive system along with electrical sensing circuits located on the wiper drive system to provide feedback information relating to the position of the wiper blades on the windshield. These sensing circuits typically employ switches which can be vulnerable to excessive current conditions especially when an over current condition exist when the wiper blade is restricted in the vicinity of the park position on the windshield. This "over current near park" condition commonly occurs when there is snow or ice buildup along the outlying portion of the windshield wiper stroke. When this snow block condition occurs, the wiper control system tends to cycle the switches responsible for sensing the position of the wiper arm. This cycling causes the switches to move along leading edges of the switch cam which in turn tends to induce arcing between the switch contacts resulting in excessive heat buildup which eventually destroys the switch contacts or melts the plastic which commonly forms the substrate which carries many of the electrical switch components and other drive components found in windshield wiper systems.
Accordingly, it is an object of this invention to set forth a windshield wiper control system consisting of a DC motor and a control circuit wherein the DC motor is prohibited from drawing excessively high currents which would otherwise destroy the DC motor or its control circuitry.
It is also an object of this invention to set forth a over current protection circuit for a windshield wiper system of a vehicle wherein only the park mode of operation is affected by the over current circuit and the remaining wiping modes (high speed, low speed, and intermittent) are not affected by the over current protection circuit.